Fixing device and image forming apparatus incorporating same

ABSTRACT

A fixing device includes a nip formation pad, an endless fixing rotator, a pressure rotator, and a lubricant transfer portion. The endless fixing rotator has an inner circumferential surface adhered with a lubricant. The pressure rotator is pressed against the nip formation pad via the fixing rotator to form a nip through which an image is fixed on a recording medium. The lubricant transfer portion transfers the lubricant toward a center side in a width direction perpendicular to a rotational direction of the fixing rotator.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2016-133504, filed onJul. 5, 2016 in the Japan Patent Office, the entire disclosure of whichis hereby incorporated by reference herein.

BACKGROUND Technical Field

Aspects of this disclosure relate to a fixing device and an imageforming apparatus incorporating the fixing device.

Related Art

A fixing device is known that includes an endless fixing rotator with alubricant adhering to an inner circumferential surface of the fixingrotator, a nip formation pad, and a pressure rotator pressed against thenip formation pad with the fixing rotator interposed between thepressure rotator and the nip formation pad to form a fixing nip. Thefixing device fixes an image on a recording medium passing through thefixing nip.

SUMMARY

In an aspect of the present disclosure, there is provided a fixingdevice that includes a nip formation pad, an endless fixing rotator, apressure rotator, and a lubricant transfer portion. The endless fixingrotator has an inner circumferential surface adhered with a lubricant.The pressure rotator is pressed against the nip formation pad via thefixing rotator to form a nip through which an image is fixed on arecording medium. The lubricant transfer portion transfers the lubricanttoward a center side in a width direction perpendicular to a rotationaldirection of the fixing rotator.

In another aspect of the present disclosure, there is provided an imageforming apparatus that includes an image bearer, an image formingdevice, a transfer device, and a fixing device. The image forming deviceforms a toner image on the image bearer. The transfer device transfersthe toner image from the image bearer onto a recording medium. Thefixing device fixes the toner image on the recording medium. The fixingdevice includes a nip formation pad, an endless fixing rotator, apressure rotator, and a lubricant transfer portion. The endless fixingrotator has an inner circumferential surface adhered with a lubricant.The pressure rotator is pressed against the nip formation pad via thefixing rotator to form a nip through which the image is fixed on therecording medium. The lubricant transfer portion transfers the lubricanttoward a center side in a width direction perpendicular to a rotationaldirection of the fixing rotator.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of thepresent disclosure would be better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view of an entire configuration of an imageforming apparatus according to an embodiment of the present disclosure;

FIG. 2 is a schematic view of a fixing device according to an embodimentof the present disclosure;

FIG. 3 is a perspective view of a portion of a nip formation padaccording to an embodiment of the present disclosure;

FIG. 4 is a schematic view of the nip formation pad and the pressureroller seen from a direction of the rotation shaft of the pressureroller;

FIG. 5 is a plan view of a comparative example of the nip formation pad;

FIG. 6 is a plan view of the nip formation pad with inclined groovesaccording to an embodiment of the present disclosure;

FIG. 7 is a schematic view of another example of the inclined grooves;

FIG. 8A is a schematic view of still another example of the inclinedgrooves;

FIG. 8B is a schematic view of still yet another example of the inclinedgrooves; and

FIG. 9 is a schematic view of still further, yet another example of theinclined grooves.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve similar results.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

Although the embodiments are described with technical limitations withreference to the attached drawings, such description is not intended tolimit the scope of the disclosure and all of the components or elementsdescribed in the embodiments of this disclosure are not necessarilyindispensable.

Below, a description is given of an electrophotographic image formingapparatus 100 as an image forming apparatus according to an embodimentof the present disclosure.

FIG. 1 is a cross-sectional view of an entire configuration of the imageforming apparatus 100. As illustrated in FIG. 1, the image formingapparatus 100 has a tandem configuration in which photoconductive drums103Y, 103C, 103M, and 103Bk are arranged side by side. Thephotoconductive drums 103Y, 103C, 103M, and 103Bk serve as image bearersto bear toner images of separated colors of yellow (Y), cyan (C),magenta (M), and black (Bk), respectively. Note that the image formingapparatus according to an embodiment of the present disclosure is notlimited to such a tandem image forming apparatus, but may have anotherconfiguration. The image forming apparatus according to an embodiment ofthe present disclosure is not also limited to a color image formingapparatus, but may be another type of image forming apparatus. Forexample, the image forming apparatus according to an embodiment may be acopier, a facsimile machine, or a multifunction peripheral having one ormore capabilities of these devices.

Process cartridges 101Y, 101C, 101M, and 101Bk for yellow (Y), cyan (C),magenta (M), and black (Bk) are detachably attached to the image formingapparatus 100. An apparatus body 100A of the image forming apparatus 100is constituted of a housing to accommodate various components. Also, thehousing includes a conveyance passage, defined by internal components ofthe image forming apparatus 100, along which a sheet as a recordingmedium is conveyed from a sheet feeding device 109 to a sheet ejectionunit 110. Toner bottles are removably mounted below a sheet ejectiontray 110 a in the apparatus body 100A. The removable toner bottlescontain color toners of yellow, cyan, magenta, and black. The apparatusbody 100A also includes a waste toner container having an inletconnected to a toner delivery tube. The waste toner container receiveswaste toner delivered through the toner delivery tube.

The optical writing device 102 includes a semiconductor laser as a lightsource, a coupling lens, an f-θ lens, a toroidal lens, a deflectionmirror, and a polygon mirror. The optical writing device 102 emits laserbeams Lb for yellow, cyan, magenta, and black onto the photoconductivedrums 103Y, 103C, 103M, and 103Bk included in the process cartridges101Y, 101C, 101M, and 101Bk to form electrostatic latent images on thephotoconductive drums 103Y, 103C, 103M, and 103Bk. Image data carried inthe laser beams Lb to be emitted are composed of single color image dataof yellow, cyan, magenta, and black, into which a desired full colorimage is separated.

In the present embodiment, an imaging unit includes four processcartridges 101Y, 101C, 101M, and 101Bk. For example, the processcartridge 101Y to form an yellow toner image includes thephotoconductive drum 103Y, a charging roller 104Y, a developing device105Y, and a cleaning blade 106Y. In the process cartridge 101Y,charging, optical writing, developing, transfer, cleaning, anddischarging processes are performed in this order.

First, the charging roller 104Y electrostatically charges an outercircumferential surface of the photoconductive drum 103Y. The opticalwriting device 102 conducts optical writing on the charged outercircumferential surface of the photoconductive drum 103Y to form anelectrostatic latent image constituted of electrostatic patterns on thephotoconductive drum 103Y. The developing device 105Y supplies andadheres yellow toner to the electrostatic latent image formed on thephotoconductive drum 103Y, thereby developing the electrostatic latentimage with the yellow toner into a visible yellow toner image. Theyellow toner image is primarily transferred onto the transfer device107. Thereafter, the cleaning blade 106Y removes residual toner from thephotoconductive drum 103Y, rendering the photoconductive drum 103Y to beready for a next primary transfer. Finally, the discharging process isperformed to remove residual static electricity from the photoconductivedrum 103Y.

The photoconductive drum 103Y includes a photoconductive layer made ofan inorganic or organic photoconductor on a cylindrical surface androtates at a linear velocity. The charging roller 104Y presses againstthe outer circumferential surface of the photoconductive drum 103Y androtates with the rotation of the photoconductive drum 103Y. A highvoltage power supply applies a direct current (DC) bias or asuperimposed bias, in which an alternating current (AC) is superimposedon the direct current, to the charging roller 104Y, thus uniformlycharging the outer circumferential surface of the photoconductive drum103Y at a given surface electric potential. The developing device 105Yincludes a supply section to supply yellow toner to the photoconductivedrum 103Y and a developing section to adhere yellow toner to thephotoconductive drum 103Y. The cleaning blade 106Y includes an elasticband made of, e.g., rubber, and a toner remover such as a brush. Theremovable developing device 105Y is housed in the apparatus body 100A.

Each of the process cartridges 101C, 101M, and 101Bk has a configurationsimilar to, even if not the same as, the configuration of the processcartridge 101Y. Toner images of cyan, magenta, and black are transferredfrom the process cartridges 101C, 101M, and 101Bk, respectively, to thetransfer device 107.

The transfer device 107 includes a transfer belt 107 a, a driving roller107 b, a tension roller 107 c, primary transfer rollers 107 dY, 107 dC,107 dM, and 107 dBk, and a secondary transfer roller 107 e. The transferbelt 107 a is an endless-shaped belt, which has no terminal end,stretched taut between and around the driving roller 107 b and thetension roller 107 c. As the driving roller 107 b and the tension roller107 c rotate, the transfer belt 107 a rotates, or moves in cycles, in arotational direction indicated by arrow A in FIG. 1.

The transfer belt 107 a contacts the process cartridges 101Y, 101C,101M, and 101Bk at area of contacts to form primary transfer nipsbetween the transfer belt 107 a and the process cartridges 101Y, 101C,101M, and 101Bk, respectively. The primary transfer rollers 107 dY, 107dC, 107 dM, and 107 dBk area applied with transfer biases of +400 V to+2500 V from a single high voltage power supply to form transferelectric fields. The secondary transfer roller 107 e presses an outercircumferential surface of the transfer belt 107 a, thereby pressingagainst the driving roller 107 b via the transfer belt 107 a. Thus, anarea of contact, herein called a secondary transfer nip, is formedbetween the secondary transfer roller 107 e and the transfer belt 107 a.

The belt cleaning device 108 is disposed between the secondary transfernip and the process cartridge 101Y in the rotational direction A of thetransfer belt 107 a. The belt cleaning device 108 includes a tonerremover and the toner conveyance tube. The toner remover removesresidual toner, which remains on the outer circumferential surface ofthe transfer belt 107 a, from the transfer belt 107 a. The residualtoner thus removed is conveyed as waste toner through the tonerconveyance tube to the waste toner container.

The sheet feeding device 109 is disposed at a lower part of theapparatus body 100A and includes a sheet tray 109 a and a sheet feedingroller 109 b. The sheet tray 109 a accommodates recording sheets ofpaper P (hereinafter, sheets P) as recording media. The sheet feedingroller 109 b picks up an uppermost sheet P from the sheets P on sheettray 109 a sheet by sheet, and feeds the uppermost sheet P to theconveyance passage.

A sheet ejection unit 110 disposed above the optical writing device 102and atop the apparatus body 100A. The sheet ejection unit 110 includes asheet ejection tray 110 a and a sheet ejection roller pair 110 b. Thesheet ejection roller pair 110 b ejects a sheet P bearing an image ontothe sheet ejection tray 110 a. In sheet ejection unit 110, sheets Pejected from the conveyance passage by the sheet ejection roller pair110 b are stacked one on another.

A registration roller pair 111 adjusts conveyance of the sheet P alongthe conveyance passage, after the sheet P is fed by the sheet feedingroller 109 b of the sheet feeding device 109.

For example, a registration sensor is interposed between the sheetfeeding roller 109 b and the registration roller pair 111 on theconveyance passage inside the apparatus body 100A to detect a leadingend of the sheet P conveyed along the conveyance passage. When apredetermined time elapses after the registration sensor detects theleading end of the sheet P, the registration roller pair 111 interruptsrotation to temporarily halt the sheet P that comes into contact withthe registration roller pair 111. The registration roller pair 111 istimed to resume rotation while sandwiching the sheet P to convey thesheet P to the secondary transfer nip. For example, the registrationroller pair 111 resumes rotation in synchronization with a compositecolor toner image, constituted of the toner images of yellow, cyan,magenta, and black superimposed one atop another on the transfer belt107 a, reaching the secondary transfer nip as the transfer belt 107 arotates in the rotation direction A.

A toner mark sensor 112 is disposed at a position opposing the transferbelt 107 a stretched over a circumferential surface of the tensionroller 107 c. The toner mark sensor 112 measures the densities of tonerimages and the positions of colors on the transfer belt 107 a with aspecular reflection sensor or a diffuse sensor, and adjusts the imagedensities and color registration.

Below, a description is given of an operation of the image formingapparatus 100 with reference to FIG. 1. As an image forming operationstarts in the image forming apparatus 100, a drying device drives androtates the photoconductive drums 103Y, 103C, 103M, and 103Bk of theprocess cartridges 101Y, 101C, 101M, and 101Bk, respectively, in aclockwise direction in FIG. 1. The charging rollers 104Y, 104C, 104M,and 104Bk uniformly charge the outer circumferential surfaces of thephotoconductive drums 103Y, 103C, 103M, and 103Bk at a predeterminedpolarity.

The optical writing device 102 emits laser beams Lb onto the chargedouter circumferential surfaces of the photoconductive drums 103Y, 103C,103M, and 103Bk according to yellow, cyan, magenta, and black imagedata, respectively, to form electrostatic latent images on the surfacesof the photoconductive drums 103Y, 103C, 103M, and 103Bk. Image dataoptically written on the photoconductive drums 103Y, 103C, 103M, and103Bk are single-color image data of yellow, cyan, magenta, and blackinto which a desired full-color image is separated. The developingdevices 105Y, 105C, 105M, and 105Bk supply toner of yellow, cyan,magenta, and black to the electrostatic latent images formed on thephotoconductive drums 103Y, 103C, 103M, and 103Bk, respectively, therebydeveloping the electrostatic latent images into visible toner images ofyellow, cyan, magenta, and black, respectively.

As a driving device drives and rotates the driving roller 107 b in acounterclockwise direction in FIG. 1, the driving roller 107 b rotatesthe transfer belt 107 a in the rotational direction A in FIG. 1. A powersupply applies a voltage controlled at a constant voltage or current andhaving a polarity opposite a polarity of the charged toner to each ofthe primary transfer rollers 107 dY, 107 dC, 107 dM, and 107 dBk. Thus,transfer electric fields are formed at the primary transfer nips formedbetween the primary transfer rollers 107 dY, 107 dC, 107 dM, and 107 dBkand the photoconductive drums 103Y, 103C, 103M, and 103Bk, respectively.The transfer electric fields generated at the primary transfer nipstransfer the yellow, magenta, cyan, and black toner images from thephotoconductive drums 103Y, 103C, 103M, and 103Bk onto the transfer belt107 a so that the yellow, magenta, cyan, and black toner images aresuperimposed one on another on the transfer belt 107 a. Thus, acomposite color toner image is formed on the outer circumferentialsurface of the transfer belt 107 a.

After the primary transfer of the toner images of yellow, cyan, magenta,and black from the photoconductive drums 103Y, 103C, 103M, and 103Bkonto the transfer belt 107 a, the cleaning blades 106Y, 106C, 106M, and106Bk remove residual toner, which remain on the photoconductive drums103Y, 103C, 103M, and 103Bk, from the photoconductive drums 103Y, 103C,103M, and 103Bk. Thereafter, dischargers discharge the outercircumferential surfaces of the photoconductive drums 103Y, 103C, 103M,and 103Bk, initializing the surface potential of the photoconductivedrums 103Y, 103C, 103M, and 103Bk, and rendering the photoconductivedrums 103Y, 103C, 103M, and 103Bk to be ready for the next imageformation.

As an image forming operation starts for forming a toner image with thedeveloping devices 105Y, 105C, 105M, and 105Bk supplying toner to theelectrostatic latent images on the photoconductive drums 103Y, 103C,103M, and 103Bk, the sheet feeding roller 109 b disposed at the lowerpart of the apparatus body 100A starts rotation. The sheet feedingroller 109 b picks up and feeds an uppermost sheet P of a plurality ofsheets P on the sheet tray 109 a of the sheet feeding device 109 to theconveyance passage. The registration roller pair 111 is timed to conveythe sheet P, thus sent to the conveyance passage by the sheet feedingroller 109 b, to the secondary transfer nip formed between the secondarytransfer roller 107 e and the transfer belt 107 a. The secondarytransfer roller 107 e is applied with a transfer voltage having apolarity opposite a polarity of the charged yellow, cyan, magenta, andblack toners formed on the transfer belt 107 a, thus forming a transferelectric field at the secondary transfer nip.

The transfer electric field secondarily transfers the toner images ofyellow, cyan, magenta, and black constructing the composite color tonerimage from the transfer belt 107 a onto the sheet P collectively. Thesheet P bearing the composite color toner image is conveyed to a fixingdevice 120 where a fixing belt 121 and a pressure roller 126 form afixing nip N. Thus, the composite color toner image is fixed on thesheet P. As the sheet P is conveyed through the fixing nip N, the fixingbelt 121 applies heat to the sheet P. At the same time, the pressureroller 126 exerts pressure on the sheet P, together with the fixing belt121.

The sheet P bearing the fixed color toner image is ejected by the sheetejection roller pair 110 b onto the outside of the apparatus body 100Aand stacked on the sheet ejection tray 110 a. Accordingly, a series ofimage forming processes performed in the image forming apparatus 100 iscompleted.

After the secondary transfer of the full color toner image from thetransfer belt 107 a onto the sheet P, the belt cleaning device 108removes residual toner, which is failed to be transferred onto the sheetP and remains on the transfer belt 107 a, from the transfer belt 107 a.The removed toner is conveyed and collected into the waste tonercontainer.

Next, a description is provided of the fixing device according to anembodiment of the present disclosure. FIG. 2 is a schematic view of thefixing device 120 according to an embodiment of the present disclosure.As illustrated in FIG. 2, the fixing device 120 includes, e.g., thefixing belt 121 as a fixing rotator, a heater 122 as a heat source, anip formation pad 123, a reinforcement 124, a thermal conductor 125, thepressure roller 126 as a pressure rotator, a holder 127, and an elasticmember 128. The fixing device 120 includes a controller 200 to conducttemperature control of, e.g., fixing temperature according to atemperature detected with a temperature sensor 129 that measures thetemperature of fixing belt 121.

After the composite color toner image is transferred from the transferbelt 107 a to the sheet P at the secondary transfer nip, the sheet P isconveyed to the fixing device 120. When the sheet P passes the fixingnip N between the fixing belt 121 and the pressure roller 126, thefixing device 120 applies heat and pressure to the sheet P to fix thecomposite color toner image on the sheet P. As the sheet P bearing thefixed toner image is discharged from the fixing nip N, the sheet Pseparates from the fixing belt 121 and is conveyed to the sheet ejectionroller pair 110 b along the conveyance passage.

The fixing belt 121 rotates in a rotational direction indicated by arrowB2 in FIG. 2 in accordance with rotation of the pressure roller 126 in arotational direction indicated by arrow B1 in FIG. 2. The fixing belt121 is driven by the pressure roller 126 as a driving source. The fixingbelt 121 and the pressure roller 126 rotate, thereby conveying the sheetP entering the fixing nip N in a sheet conveyance direction B3, anddischarging the sheet P from the fixing nip N. The sheet conveyancedirection B3 serves as a recording medium conveyance direction.

A description is given of a construction of the pressure roller 126. Thepressure roller 126, having a diameter in a range of from about 20 mm toabout 40 mm, is constructed of a hollow cored bar 126 a and an elasticlayer 126 b around the cored bar 126 a. A rotation shaft of the pressureroller 126 is pressed toward the nip formation pad 123 via the holder127 by the elastic member 128. The elastic layer 126 b is made ofsilicone rubber foam, silicone rubber, fluoro rubber, or the like.Optionally, the pressure roller 126 may further include a thin releaselayer coating the elastic layer 126 b and being made oftetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA),polytetrafluoroethylene (PTFE), or the like. The pressure roller 126 ispressed against the fixing belt 121 to form the desired fixing nip Nbetween the pressure roller 126 and the fixing belt 121. A driving gearis mounted on an axial end of the pressure roller 126, and the pressureroller 126 is rotated and driven in the rotational direction B1 in FIG.2. Optionally, a heater, such as a halogen heater, may be disposedinside the pressure roller 126.

The fixing belt 121 is a free belt not stretched and an endless, thinflexible belt. The fixing belt 121 receives a driving force from thepressure roller 126 to rotate (travel) in the rotational direction B2 inFIG. 2. The fixing belt 121 is constructed of a base layer constitutingthe inner circumferential surface, an elastic layer coating the baselayer, and a release layer coating the elastic layer, which produce atotal thickness of the fixing belt 121 not greater than 500 μm. The baselayer, the elastic layer, and the release layer are stacked in thisorder from the side of an inner circumferential surface being a slidesurface of the fixing belt 121 that slides the nip formation pad 123.The base layer, having a thickness in a range of from 30 μm to 100 μm,is made of a resin material, such as polyimide. Use of the resinmaterial provides the base layer with low stiffness. Such aconfiguration allows the fixing belt 121 to more easily wind in an areadownstream from an exit of the fixing nip N in the rotational directionB2 of the fixing belt 121. The resin material can reduce the productioncost as compared to a metal material. However, the base layer may bemade of metal, such as nickel or stainless steel. The elastic layer,having a thickness in a range of from 100 μm to 300 μm, is made ofrubber such as silicone rubber, silicone rubber foam, and fluoro rubber.The elastic layer can prevent formation of slight surface asperities ofthe fixing belt 121 at the fixing nip. Accordingly, heat can beuniformly transmitted to a toner image on the sheet P, therebypreventing formation of a rough image, such as an orange peel image.

The release layer, having a thickness of from 5 μm to 50 μm, may be madeof perfluoroalkoxy polytetrafluoroethylene (PFAPTFE), polyimide (PI),polyamide imide (PAI), polyether imide (PEI), polyether sulfide (PES),polyether ether ketone (PEEK), or the like. A loop diameter of thefixing belt 121 is in a range of from 15 mm to 120 mm. According to thisexemplary embodiment, the fixing belt 121 has a loop diameter of about30 mm.

The heater 122, the nip formation pad 123, the reinforcement 124, andthe thermal conductor 125, together with, e.g., a first stay, a secondstay, and a sheet member, are disposed and fixed inside a loop formed bythe fixing belt 121. As the heater 122, a halogen heater or a carbonheater may be used, for example. The nip formation pad 123 is secured(fixed) so as to slide over the inner circumferential surface of thefixing belt 121. The nip formation pad 123 presses against the pressureroller 126 via the fixing belt 121 to form the fixing nip N, throughwhich the sheet P is conveyed. Optionally, a lubricant, such as fluorinegrease and silicone oil, may be applied between the thermal conductor125 and the fixing belt 121 to reduce abrasion of the fixing belt 121 asthe fixing belt 121 slides over the thermal conductor 125. In thepresent embodiment, the thermal conductor 125 is substantially circularin cross-section. However, in some embodiments, the thermal conductor125 may have any suitable shape in cross section, considering the closecontactness of the fixing belt 121 and the thermal conductor 125 fromviewpoints of heat transfer efficiency and sliding resistance.

The thermal conductor 125 is heated by radiation heat of the heater 122.The output of the heater 122 is controlled by a power supply unit of theapparatus body 100A. The thermal conductor 125 is a metal thermalconductor made of conductive metal, such as aluminum, iron, andstainless steel. The thermal conductor 125 has a thickness not greaterthan 0.2 mm, thus allowing effective heating of the fixing belt 121. Thethermal conductor 125 is disposed in proximity to or in contact with theinner circumferential surface of the fixing belt 121 at acircumferential span on the fixing belt 121 other than a nip formedbetween the fixing belt 121 and the nip formation pad 123. At the nip,the thermal conductor 125 includes a recess having an inwardly recessedshape with an opening.

As illustrated in FIG. 2, at an ambient temperature, a gap G (a gap at aposition other than the nip) between the fixing belt 121 and the thermalconductor 125 produced at the circumferential span on the fixing belt121 other than the nip is greater than 0 mm and not greater than 2 mm.Hence, the fixing belt 121 slides over the thermal conductor 125 in adecreased area, suppressing abrasion of the fixing belt 121 that mayaccelerate as the fixing belt 121 slides over the thermal conductor 125in an increased area. Simultaneously, the fixing belt 121 is notisolated from the thermal conductor 125 with an excessively increasedgap therebetween, suppressing degradation in heating efficiency inheating the fixing belt 121.

Additionally, the thermal conductor 125 disposed in proximity to thefixing belt 121 retains a circular shape of the flexible fixing belt121, reducing deformation and resultant degradation and breakage of thefixing belt 121. In order to decrease resistance between the thermalconductor 125 and the fixing belt 121 sliding thereover, a slide face,that is, an outer circumferential surface, of the thermal conductor 125may be made of a material having a decreased friction coefficient or theinner circumferential surface of the fixing belt 121 may be coated witha surface layer made of a material containing fluorine. If the fixingdevice 120 includes a separate component that conducts heat from theheater 122 to the fixing belt 121 evenly and stabilizes motion of thefixing belt 121 as the fixing belt 121 is driven, the fixing device 120may employ a direct heating method in which the heater 122 heats thefixing belt 121 directly without the thermal conductor 125. In thiscase, the fixing device 120 reduces its total thermal capacity by athermal capacity of the thermal conductor 125, heating the fixing belt121 quickly and saving energy.

The output of the heater 122 is controlled based on the temperature ofthe outer circumferential surface of the fixing belt 121 detected by thetemperature sensor 129. The temperature sensor 129 includes, e.g., athermistor disposed opposite the outer circumferential surface of thefixing belt 121. Thus, the fixing belt 121 is heated to a desired fixingtemperature by the heater 122 controlled as described above.

A description is provided of a fixing operation performed by the fixingdevice 120 having the construction described above. As the image formingapparatus 100 is powered on, the heater 122 is supplied with power andthe driving device starts driving and rotating the pressure roller 126in the rotational direction B1 in FIG. 2. The fixing belt 121 is drivenand rotated the rotational direction B2 in FIG. 2 by friction betweenthe fixing belt 121 and the pressure roller 126. Then, the sheet feedingroller 109 b picks up and feeds a sheet P from the sheet tray 109 a tothe registration roller pair 111 that conveys the sheet P to thesecondary transfer nip where an unfixed color toner image is secondarilytransferred from the transfer belt 107 a onto the sheet P at theposition of the secondary transfer roller 107 e. The sheet P bearing theunfixed toner image is conveyed in a direction indicated by arrow B3 inFIG. 2 while guided by a guide plate, and enters the fixing nip N formedbetween the fixing belt 121 and the pressure roller 126 pressed againstthe fixing belt 121. The heat of the heater 122 is conducted to thethermal conductor 125. The toner image is fixed on the surface of thesheet P under the heat of the fixing belt 121 heated by the thermalconductor 125 and the pressure of the nip formation pad 123 and thepressure roller 126 reinforced by the reinforcement 124. Then, the sheetP sent from the fixing nip N is conveyed in a direction indicated byarrow B4 in FIG. 2. Thus, the fixing device 120 completes a series offixing processes.

FIG. 3 is a perspective view of a portion of the nip formation pad inthe present embodiment. FIG. 4 is a schematic view of the nip formationpad and the pressure roller seen from a direction of the rotation shaftof the pressure roller. FIG. 5 is a plan view of a comparative exampleof the nip formation pad. FIG. 6 is a plan view of the nip formation padin the present embodiment.

As illustrated in FIGS. 3 and 4, the slide face of the nip formation pad123 is coated with ceramic coating 123 a to reduce the slidingresistance against the fixing belt 121. Fluorine grease 123 b as alubricant is also adhered to the slide face of the nip formation pad123. Such a configuration can reduce the sliding resistance of the nipformation pad 123 against the fixing belt 121 and the abrasion of theinner circumferential surface of the fixing belt 121 made of a resinmaterial. The ceramic coating 123 a is coated at a thickness of from 10μm to 30 μm.

Seen from a width direction, indicated by arrow W in FIGS. 5 and 6,perpendicular to the rotational direction B2 of the fixing belt 121, thepressure roller 126 is pressed against an upstream end of the nipformation pad 123, which has the slide face against the fixing belt 121,in the rotational direction B2 of the fixing belt 121 and deforms to becompressed in a thickness direction of the pressure roller 126. Thus,the pressure roller 126 is temporarily separated from the slide face ofthe nip formation pad 123. As the pressure roller 126 further rotatestoward a downstream side in the rotational direction B2 of the fixingbelt 121, the pressure roller 126 gradually restores and slides over theslide face of the nip formation pad 123 to be compressed. The load ofthe pressure roller 126 on the nip formation pad 123 is largest in anarea near the exit of the fixing nip N at the downstream side of the nipformation pad 123 in the rotational direction B2 of the fixing belt 121.

Accordingly, as illustrated in FIG. 5, the fluorine grease 123 badhering to the inner circumferential surface of the fixing belt 121 isless likely to flow toward the downstream side in the rotationaldirection B2 of the fixing belt 121 in an area near an exit of a niparea 131 a corresponding to the nip formed by the fixing belt 121 andthe nip formation pad 123. Accordingly, as a subsequent portion of thefluorine grease 123 b flows into the area near the exit of the nip area131 a, the amount of the fluorine grease 123 b remaining on the areagradually increases. An excessive portion of fluorine grease 123 b movesto the width direction perpendicular to the rotational direction B2 ofthe fixing belt 121. Such excessive fluorine grease may leak from endsof the nip formation pad 123 in the width direction over time.Consequently, the total amount of the fluorine grease 123 b adhering tothe fixing belt 121 may decrease, thus increasing the sliding resistanceof the nip formation pad 123 against the fixing belt 121. As a result,it may be difficult to obtain high durability.

For example, as illustrated in FIG. 2, the area of the nip formation pad123 near the exit of the fixing nip N has a circular shape along theouter circumferential surface of the pressure roller 126 to facilitatethe separation of the sheet P. Accordingly, in the area near the exit ofthe nip area 131 a, the load of the pressure roller 126 against the nipformation pad 123 more increases. Consequently, the amount of fluorinegrease 123 b leaking from an end of the nip formation pad 123 in thewidth direction increases over time, thus increasing the speed ofdecreasing the total amount of fluorine grease 123 b adhering to theinner circumferential surface of the fixing belt 121. As a result, thesliding resistance of the nip formation pad 123 against the fixing belt121 would rapidly increase.

To prevent such an increase in sliding resistance, as illustrated inFIG. 6, a plurality of inclined grooves 140 inclined from each end to acenter in the width direction is formed on a face of the nip formationpad 123 corresponding to an area (an exit area 131 c) near the exit ofthe nip area 131 a at the downstream side in the rotational direction B2of the fixing belt 121. On the other hand, such inclined grooves are notformed on a face of the nip formation pad 123 corresponding to an area(an entry area 131 b) near the entry of the nip area 131 a at theupstream side in the rotational direction B2 of the fixing belt 121.With such a configuration, the fluorine grease 123 b between the innercircumferential surface of the fixing belt 121 and the nip formation pad123 is temporarily reserved in groove portions of the inclined grooves140. The reserved fluorine grease 123 b flows along the groove portionsof the inclined grooves 140 toward the center in the width direction,thus suppressing leakage of the fluorine grease 123 b from ends of thenip formation pad 123 in the width direction. Accordingly, the totalamount of fluorine grease 123 b adhering to the inner circumferentialsurface of the fixing belt 121 can be maintained. Note that a slide-faceedge portion of the inclined groove 140 formed on the nip formation pad123, in particular, a boundary portion between an inner wall of thegroove facing the upstream side in the rotational direction B2 of thefixing belt 121 and the slide face of the nip formation pad 123 may havea curved surface (see FIG. 8B), thus suppressing the abrasion of theinner circumferential surface of the fixing belt 121 and the increase insliding resistance.

As illustrated in FIG. 6, each of the plurality of inclined grooves 140is longer in the rotational direction B2 of the fixing belt 121 than inthe width direction perpendicular the rotational direction B2 of thefixing belt 121. Such a configuration can reserve the fluorine grease123 b moved to ends in the width direction in the plurality of inclinedgrooves 140, thus allowing the fluorine grease 123 b to be moreeffectively returned to the center in the width direction.

Note than, as illustrated in FIGS. 7, 8, and 9, the depth of the grooveportion of the inclined groove 140 gradually decreases from the upstreamside toward the downstream side in the rotational direction B2 of thefixing belt 121. Such a configuration allows the fluorine grease tosmoothly flow out the groove portion of the inclined groove 140, thusallowing the fluorine grease to more effective adhere to the innercircumferential surface of the fixing belt 121. The ends of the inclinedgroove 140 in the rotational direction B2 of the fixing belt 121 arecontinuous with the slide face of the nip formation pad 123 against thefixing belt 121. Thus, the inclined grooves 140 serve as lubricanttransfer portions. Such a configuration allows all the fluorine greasetemporarily remaining in the inclined grooves 140 to smoothly flow outthe inclined grooves 140, thus allowing the fluorine grease to moreeffectively adhere to the inner circumferential surface of the fixingbelt 121. The bottom shape of the inclined groove 140 in cross sectionin the thickness direction of the inclined groove 140 is, for example, atriangular shape illustrated in FIG. 7 or a flat shape illustrated inFIG. 8A. As illustrated in FIG. 9, an inner wall of the inclined groove140 may be inclined in the rotational direction B2 of the fixing belt121 only at one side in the width direction perpendicular the rotationaldirection B2 of the fixing belt 121. The mechanism of moving thefluorine grease toward the center of the nip formation pad 123 in thewidth direction is not limited to the above-described inclined groovebut, for example, may be a guide formed of guide walls or projectionsinclined from the ends to the center of the nip formation pad in thewidth direction.

The exemplary embodiments described above are one example and attainadvantages below in a plurality of aspects A to J.

Aspect A

A fixing device, such as the fixing device 120, includes an endlessfixing rotator, such as the fixing belt 121, having an innercircumferential surface adhered with a lubricant; a nip formation pad,such as the nip formation pad 123; a pressure rotator, such as thepressure roller 126, pressed against the nip formation pad via thefixing rotator to form a nip through which an image is fixed on arecording medium; and a lubricant transfer portion, such as the inclinedgrooves 140, to transfer the lubricant toward a center side in a widthdirection perpendicular to a rotational direction of the fixing rotator.Generally, according to the fixing device, since the nip is favorablyformed, at least one of the pressure rotator and the fixing rotatorincludes an elastic layer. For example, when the pressure rotator havingthe elastic layer is seen from the width direction perpendicular to therotational direction of the fixing rotator, the pressure rotator ispressed against an upstream end of the nip formation pad, which has aslide face against the fixing rotator, in the rotational direction ofthe fixing rotator in fixing and deforms to be compressed in a thicknessdirection of the pressure rotator. As the pressure rotator moves to thedownstream side from the end in the rotational direction of the fixingrotator, the pressure rotator gradually restores. The load of thepressure rotator against the nip formation pad in the nip increases asthe pressure rotator approached an area near the exit of the nipformation pad at the downstream side in the rotational direction of thefixing rotator. Accordingly, the lubricant adhering to the innercircumferential surface of the fixing rotator less easily flowsdownstream in the rotational direction of the fixing rotator near theexit of the nip. Since subsequent lubricant flows to the area near thenip, the amount of the lubricant remaining on the area graduallyincreases. An excessive lubricant moves in the width directionperpendicular to the rotational direction of the fixing rotator. Suchexcessive lubricant may leak from an end of the nip formation pad in thewidth direction over time. Consequently, the total amount of thelubricant adhering to fixing rotator may decrease, thus increasing thesliding resistance of the nip formation pad against the fixing rotator.In the present aspect, the lubricant transfer portion transfers thelubricant to the center side in the width direction perpendicular to therotational direction of the fixing rotator. Such a configuration canreturn the lubricant, which has moved to ends in the width direction, tothe center side, thus reducing leakage of the lubricant from ends of thenip formation pad in the width direction. Accordingly, the decrease inthe total amount of the lubricant adhering to the inner circumferentialsurface of the fixing rotator is suppressed, thus suppressing theincrease in the sliding resistance of the nip formation pad against thefixing rotator. Thus, a reduction in slide performance of the fixingrotator and the nip formation pad can be suppressed.

Aspect B

In aspect A, the lubricant transfer portion includes a groove, such asthe inclined groove 140, on a face of the nip formation pad opposing thefixing rotator at a downstream side from the nip in the rotationaldirection of the fixing rotator. In a direction from an upstream side toa downstream side of the groove in the rotational direction of thefixing rotator, the groove is inclined from an end side to the centerside of the nip formation pad in the width direction. With such aconfiguration, the lubricant having moved toward axial ends of the nipformation pad is reserved by the groove. The lubricant flows along thegroove and is transferred from an end side to the center side. Thus,leakage of the lubricant from ends in the width direction can besuppressed, thus reducing the decrease in the total amount of thelubricant.

Aspect C

In aspect B, as the groove, a plurality of grooves is arranged in thewidth direction perpendicular to the rotational direction of the fixingrotator. With such a configuration, the lubricant adhering to the innercircumferential surface of the fixing rotator is segmented and retainedby a plurality of grooves, thus allowing the lubricant to be evenlyspread in the width direction of the nip. Accordingly, a reduction inslide performance of the fixing rotator and the nip formation pad can befurther suppressed.

Aspect D

In any of aspects A to C, a downstream end of the nip formation pad inthe nip in the rotational direction of the fixing rotator has a circularshape along an outer circumferential surface of the pressure rotator.Such a configuration facilitates winding of a recording sheet afterfixing and enhances the separation performance of the recording medium.

Aspect E

In any of aspects B to D, the groove is longer in the rotationaldirection of the fixing rotator than in the width direction. Such aconfiguration allows the lubricant having moved to ends in the widthdirection to be reserved in a larger number of grooves, thus effectivelyreturning the lubricant to the center in the width direction.

Aspect F

In any of aspects B to E, a downstream end of the groove in therotational direction of the fixing rotator is continuous with a slideface of the nip formation pad that slides over the fixing rotator. Sucha configuration allows all the grease reserved in the groove to smoothlyflow out the groove, thus allowing the grease to more effectively adhereto the inner circumferential surface of the fixing rotator.

Aspect G

In any of aspects B to F, a boundary portion between an inner wall ofthe groove facing an upstream side in the rotational direction of thefixing rotator and a slide face of the nip formation pad has a curvedsurface. Such a configuration can suppress the abrasion of the innercircumferential surface of the fixing rotator and an increase in slidingresistance.

Aspect H

In any of aspects B to G, the depth of the groove gradually decreasesfrom an upstream side to a downstream side in the rotational directionof the fixing rotator. Such a configuration allows the lubricantreserved in the groove to favorably flow out the groove, thus allowingthe lubricant to more effectively adhere to the inner circumferentialsurface of the fixing rotator.

Aspect I

In any of aspects A to H, the lubricant is fluorine grease.

Aspect J

An image forming apparatus, such as the image forming apparatus 100,includes an image bearer, such as the transfer belt 107 a; an imageforming device, such as the process cartridges 101Y, 101C, 101M, and101Bk, to form a toner image on the image bearer; a transfer device,such as the transfer device 107, to transfer the toner image from theimage bearer onto a recording medium; and a fixing device, such as thefixing device 120, to fix the toner image on the recording medium. Thefixing device is the fixing device according to any of aspects A to I.According to the present aspect, leakage of the lubricant can besuppressed, thus suppressing a reduction in lubricating performance ofthe lubricant. Accordingly, a reduction in slide performance of thefixing rotator and the nip formation pad can be suppressed, thusreducing defective rotation of the fixing rotator and allowing excellentimage formation.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it will be obvious that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

What is claimed is:
 1. A fixing device comprising: an endless fixingrotator having an inner circumferential surface adhered with alubricant; a nip formation pad disposed inside a loop of the fixingrotator; a pressure rotator pressed against the nip formation pad viathe fixing rotator to form a nip through which an image is fixed on arecording medium; and a lubricant transfer structure that includes atleast one groove to transfer the lubricant toward a center area in awidth direction perpendicular to a rotational direction of the fixingrotator, the at least one groove being disposed to extend outward fromthe center area at least to one or more outer edge of the fixing rotatorin the width direction, and an outermost end of the at least one groovein the width direction is covered by the fixing rotator.
 2. The fixingdevice according to claim 1, wherein the at least one groove of thelubricant transfer structure includes a first groove on a face of thenip formation pad opposing the fixing rotator at a downstream side fromthe nip in the rotational direction of the fixing rotator, and wherein,in a direction from an upstream side to a downstream side of the firstgroove in the rotational direction of the fixing rotator, the firstgroove is inclined from an end side to the center area in the widthdirection.
 3. The fixing device according to claim 2, wherein the atleast one groove of the lubricant transfer structure includes multiplegrooves arranged in the width direction.
 4. The fixing device accordingto claim 2, wherein the first groove is longer in the rotationaldirection of the fixing rotator than in the width direction.
 5. Thefixing device according to claim 2, wherein a downstream end of thefirst groove in the rotational direction of the fixing rotator iscontinuous with a slide face of the nip formation pad that slides overthe fixing rotator.
 6. The fixing device according to claim 2, wherein aboundary between an inner wall of the first groove opposing an upstreamside in the rotational direction of the fixing rotator and a slide faceof the nip formation pad has a curved surface.
 7. The fixing deviceaccording to claim 2, wherein a depth of the first groove graduallydecreases from an upstream side to a downstream side in the rotationaldirection of the fixing rotator.
 8. The fixing device according to claim1, wherein a downstream end of the nip formation pad in the nip in therotational direction of the fixing rotator has a circular shape along anouter circumferential surface of the pressure rotator.
 9. The fixingdevice according to claim 1, wherein the lubricant is fluorine grease.10. The fixing device according to claim 1, wherein the lubricanttransfer structure includes the at least one groove being disposed toextend outward from the center area at least to two outer edges of thefixing rotator in the width direction.
 11. The fixing device accordingto claim 1, further comprising a thermal conductor disposed and fixedinside the loop formed by the endless fixing rotator.
 12. The fixingdevice according to claim 11, wherein the thermal conductor is a metalthermal conductor.
 13. The fixing device according to claim 11, furthercomprising a heater inside the loop formed by the endless fixingrotator, to directly heat the endless fixing rotator with no thermalconductor interposed between the heater and the endless fixing rotator.14. An image forming apparatus comprising: an image bearer; an imageforming device to form a toiler image on the image bearer; a transferdevice to transfer the toner image from the image bearer onto arecording medium; and a fixing device to fix the toner image on therecording medium, the fixing device including: a nip formation pad; anendless fixing rotator having an inner circumferential surface adheredwith a lubricant; a pressure rotator pressed against the nip formationpad via the fixing rotator to form a nip through which the image isfixed on the recording medium; and a lubricant transfer structure thatincludes at least one groove to transfer the lubricant toward a centerarea in a width direction perpendicular to a rotational direction of thefixing rotator, the at least one groove being disposed to extend outwardfrom the center area at least to an outer edge of the fixing rotator inthe width direction, and an outermost end of the at least one groove inthe width direction is covered by the fixing rotator.